Low grade papillary urothelial carcinoma

by Jason Wasserman MD PhD FRCPC and Zuzanna Gorski MD
June 11, 2025

Low-grade papillary urothelial carcinoma is a type of cancer that begins from specialized cells lining the urinary tract. The urinary tract includes the kidneys, ureters, bladder, and urethra, with most tumours appearing in the bladder. This cancer is called low-grade because, under the microscope, the tumour cells look quite similar to normal, healthy urothelial cells. The term papillary describes the unique pattern of tumour growth, forming finger-like projections of tissue that protrude into the urinary tract.

Pathologists classify these tumours into two main types: non-invasive and invasive. This classification depends on whether cancer cells have grown into deeper layers of tissue beneath the surface lining (the urothelium). Identifying whether the tumour is invasive is important because non-invasive tumours can usually be successfully treated with surgery alone, while invasive tumours typically require additional treatments after surgery.

Understanding the urinary tract

The urinary tract is responsible for removing waste products and excess water from your body through urine. It is made up of:

• Kidneys: Organs that filter your blood to create urine.

• Ureters: Tubes that carry urine from the kidneys to the bladder.

• Bladder: A muscular organ that stores urine until it is expelled.

• Urethra: A tube through which urine exits your body.

The inner surface of the urinary tract is covered by specialized urothelial cells, forming a protective barrier called the urothelium.

What are the symptoms of low-grade papillary urothelial carcinoma?

Common symptoms include:

• Blood in the urine (hematuria), which can make urine appear pink, red, or brown.

• Pain or discomfort while urinating (dysuria).

• A frequent or urgent need to urinate.

These symptoms may vary in severity, and some people initially may not have any noticeable symptoms.

What causes low-grade papillary urothelial carcinoma?

Several factors have been linked to an increased risk of developing papillary urothelial carcinoma:

• Tobacco smoke (the strongest known risk factor).

• Occupational or environmental exposure to certain chemicals, such as benzidine dyes, opium, aromatic amines, and arsenic.

• Exposure to aristolochic acid, commonly found in some herbal medicines containing Aristolochia plants.

• Chronic inflammation or irritation of the urinary tract due to long-term catheter use or certain infections, such as the parasite Schistosoma haematobium.

• Certain medical treatments, including radiation therapy to the pelvis or chemotherapy medications such as chlornaphazine or cyclophosphamide.

Non-invasive versus invasive tumours

Non-invasive tumours

In non-invasive tumours, cancer cells are limited to the surface layer (urothelium) and do not invade deeper tissues. These tumours cannot spread to other parts of the body and are typically cured by surgery alone.

Invasive tumours

In invasive tumours, cancer cells have spread beyond the surface lining into deeper tissues, such as the lamina propria or the muscularis propria (the muscle layer of the bladder wall). Unlike non-invasive tumours, invasive tumours have the potential to spread to nearby lymph nodes and distant organs, requiring additional treatment following surgery.

When examining an invasive tumour, pathologists assess how deeply cancer cells have invaded the tissue beneath the urothelium. This information helps your healthcare team determine the pathologic tumour stage (pT), crucial for deciding treatment options.

How is this diagnosis made?

A diagnosis of low-grade papillary urothelial carcinoma usually involves multiple steps:

• Urine test: Examining a urine sample under the microscope to check for cancer cells.

• Biopsy: Taking a small tissue sample from the urinary tract, typically during a procedure called cystoscopy, for microscopic examination by a pathologist.

• Transurethral resection of bladder tumour (TURBT): A procedure performed through the urethra to remove the entire visible tumour from the bladder for diagnosis and treatment.

• Partial or complete resection: For larger or invasive tumours, a more extensive surgery might be necessary to remove part or all of the affected organ (such as the bladder or kidney).

Why is it important to sample the muscularis propria?

The muscularis propria is a thick layer of muscle within the bladder wall. When doctors remove bladder tumours, they often include some muscle tissue from this layer in the surgical sample. This is crucial because examining this muscle under the microscope allows pathologists to confirm whether cancer cells have spread into the muscle. Knowing this helps determine if the tumour is invasive, which significantly influences treatment decisions. Most pathology reports explicitly state if muscle tissue from the muscularis propria was included and examined.

Can the tumour grow back after it is removed?

Yes, it can. Approximately half (50%) of patients with low-grade papillary urothelial carcinoma experience a recurrence, meaning the tumour grows back after being removed. Additionally, some low-grade tumours may change over time into a more aggressive form called high-grade papillary urothelial carcinoma. Regular follow-up examinations and monitoring are crucial for detecting any recurrence early.

Pathologic stage (pT)

The stage of low-grade papillary urothelial carcinoma is determined using the internationally recognized TNM staging system, created by the American Joint Committee on Cancer. This system assesses:

• T (Tumour): Depth and extent of tumour invasion.

• N (Nodes): Involvement of nearby lymph nodes.

• M (Metastasis): Presence of cancer cells in distant parts of the body.

For low-grade non-invasive papillary urothelial carcinomas, the tumour stage is always designated as pTa, indicating it is non-invasive and limited strictly to the urothelial lining.

Questions to ask your doctor

• Is my tumour non-invasive or invasive?

• What are the chances of my tumour coming back after treatment?

• Will I require additional treatment beyond surgery?

• How often should I have follow-up visits and imaging tests?

• Should I make lifestyle changes to lower the risk of tumour recurrence?

• What signs or symptoms should prompt me to seek medical attention?

• Can low-grade papillary urothelial carcinoma become more aggressive over time?

• Are there family screening recommendations for this type of cancer?